1. Technical Field of the Invention
The present invention relates generally to an image-forming apparatus designed to form multi-colored images on a print sheet without any color shifts.
2. Background Art
Full color printers are known which are designed to form a multi-colored image by overlaying yellow, magenta, cyan, and block toner images in registration to a print sheet on a conveyer using a plurality of image-forming units placed in the direction of transport of the print sheet. In a printer of this type, misregistation between toner images will cause outlines off the toner images to be shifted from each other, resulting in reduction in image quality. In order to compensate for this shift, the printer prints the toner images on a conveyer belt and adjusts the interval between adjacent two of the image-forming units based on the images on the conveyer belt. It is, however, difficult to eliminate the shift between the toner images completely due to rises in temperature within the printer, of the conveyer belt itself, and of a belt drive shaft. Particularly, a fixing device usually generates a large quantity of heat, impinging upon the movement of the conveyer belt. Specifically, a print operation for a long time will cause the heat to be stored in a frame installed near the fixing device, thereby resulting in radiation of the heat to elevate the temperature of the conveyer belt and the belt drive shaft. When the print operation is turned off, the fixing device is placed in a standby mode so that the temperature thereof will be decreased. The on and off operations of the printer, thus, causes the temperature of the conveyer belt to be changed, which leads to a change in movement of the conveyer belt. The correction of a shift between toner images due to these thermal problems results in consumption of time in each print operation which will lead to a decrease in throughput.